Idiosyncratic Perception: A Link Between Acuity, Perceived Position, and Apparent Size

Abstract

Perceiving the positions of objects is a prerequisite for most other visual and visuomotor functions, but human perception of object position varies from one individual to the next. The source of these individual differences in perceived position and their perceptual consequences are unknown. Here, we tested whether idiosyncratic biases in the underlying representation of visual space propagate across different levels of visual processing. In Experiment 1, using a position matching task, we found stable, observer-specific compressions and expansions within local regions throughout the visual field. We then measured Vernier acuity (Experiment 2) and perceived size of objects (Experiment 3) across the visual field and found that individualized spatial distortions were closely associated with variations in both visual acuity and apparent object size. Our results reveal idiosyncratic biases in perceived position and size, originating from a heterogeneous spatial resolution that carries across the visual hierarchy.Accurately registering the locations of objects is a critical visual function. Most other perceptual functions including pattern and object recognition, as well as visually guided behavior, hinge on first localizing object positions. Position perception is generally assumed to be dictated by retinotopic location, and that may explain a lot of the variance in perceived position. However, perceived position can be biased due to various external factors, such as overt attention [1], motion [2] and saccadic eye movements [3]. The impact of these factors can be significant, especially considering the spatial scale at which object recognition and visually guided action happen. A 0.5-degree shift in the location of a pedestrian or car crossing a freeway could result in a catastrophic collision. The scale at which perception and action needs to operate is often very fine, and many factors bias perceived position at a scale that is behaviorally relevant.In the absence of these external factors, perceived position is often assumed to be uniformly dictated by retinotopic position. However, a recent study challenges this belief and demonstrates that people mislocalize objects idiosyncratically and consistently even without apparent change in the environment [4]. The unique biases in object locations were shown to be stable across time when tested after weeks or months, indicating a stable perceptual fingerprint of object location.Why do people perceive idiosyncratically biased object locations in different parts of the visual field and what are the perceptual consequences of it? Here, we test the possibility that variations in spatial resolution across the visual field might cause the spatial distortions in perceived position. Many researchers have shown that visual acuity varies across the visual field [5][6][7]. Because many models of localization depend implicitly or explicitly on the underlying resolution and homogeneity of spatial coding [1,[8][9][10], it is conceivable that the inhomogeneity in visual acuity could...